gain, \(G\)

of a photomultiplier
https://doi.org/10.1351/goldbook.G02572
The gain of a photomultiplier is given by the equation \(G=k\ \sigma ^{n}\), where \(k\) is the efficiency of collection of photoelectrons on the first dynode, \(\sigma \) is the secondary emission ratio, i.e. the number of secondary electrons emitted for each electron incident on the dynode and \(n\) is the number of dynodes.
Source:
PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1753 (https://doi.org/10.1351/pac199567101745)